This invention relates to a high-voltage variable resistor.
A conventional high-voltage variable resistor commonly called a focus pack which is capable of variably outputting a focus voltage and a screen voltage generally includes a circuit board generally constructed as shown in FIG. 6A. More particularly, a circuit board generally designated at reference numeral 101 in FIG. 2A has a circuit pattern 102 formed on a front surface thereof by printing. The circuit pattern includes an input electrode E1, a focus voltage output electrode E2, a screen voltage output electrode E3, a ground electrode E4, a first variable resistance pattern VR1 for adjustment or variation of a screen voltage, and a second variable resistance pattern VR2 for adjustment or variation of a screen voltage. Also, the circuit pattern 102 includes connection patterns CP1 and CP2 each acting as an electrical connection means which is contacted with a slide element (not shown) to establish electrical connection between the slide element and the output electrodes E1 and E2. The slide element includes a slide contact slid on the variable resistance patterns VR1 and VR2 and a contact rotated on ends CP11 and CP12 of the connection patterns CP1 and CP2.
A size of the high-voltage variable resistor generally depends on an area of the circuit board 101, of which a size depends on the circuit pattern 102. In determination of a size of the circuit board 101, a distance between each adjacent two of sections of the circuit pattern 102 is determined in view of so-called pattern dielectric strength (normally, 1 mm/1 kV) capable of preventing occurrence of discharge. Thus, a distance A between the variable resistance patterns VR1 and VR2 and the ends CP11 and CP12 of the connection patterns CP1 and CP2 is likewise regulated by the pattern dielectric strength. Thus, it is required to increase a radium of an arc of each of the variable resistance patterns VR1 and VR2 depending on a magnitude of a voltage applied, so that a decrease in area of the circuit board is subject to restriction.